Vehicles may recover exhaust heat for transfer to various other systems in an internal combustion engine.
For example, U.S. Pat. No. 4,107,922 describes an insulated heat pipe that transfers heat from an exhaust manifold to an exhaust gas reactor. The system includes an evaporative zone coupled to the exhaust manifold, a transport zone for transporting a working fluid, and a condensation zone coupled to the exhaust gas reactor. The system transfers heat from the exhaust manifold to the exhaust gas reactor during a warm-up phase of the engine. Further, the system may include a secondary heat pipe coupled to the insulated heat pipe adjacent to the condensation zone to balance an operating temperature of the exhaust gas reactor.
The inventors herein have recognized various issues with the above system. In particular, transferring heat to an emissions control device throughout engine operation increases a risk for thermal degradation of the emissions control device. For example, when the feed gas temperature exceeds a tolerable threshold, the engine may operate in enrichment mode (i.e., air:fuel<14.7) to reduce the risk of overheating a turbine (e.g., if the engine is a turbo engine including a compressor and a turbine) and/or a catalytic converter. Fuel consumption may increase to maintain the engine operating in enrichment mode. Further, the over rich fuel may increase emissions which may over burden the catalytic converter with trapped particulates (e.g., carbon monoxide). When oxygen is available, trapped particulates may be burned to purge the catalytic converter; however, a substrate of the catalytic converter may melt if the engine operates in enrichment mode for lengthy periods of time. Prior solutions have included a water jet to cool down the exhaust manifold and/or the turbo. However, the water jet also absorbs heat during cold start and thus delays the catalytic converter light-off. As such, emissions may increase due to hydrocarbons being ineffectively reduced by the catalytic converter.
As such, one example approach to address the above issues is to use a heat pipe and suitable phase changing materials to recover exhaust heat upstream from a catalytic converter and transfer the heat away from the exhaust system. In this way, it is possible to absorb heat from the exhaust system to reduce thermal degradation of the catalytic converter. Specifically, an evaporating region of the heat pipe is integrated with an exhaust manifold upstream from the catalytic converter. In some embodiments, an integrated exhaust manifold includes one or more heat pipes that facilitate heat transfer to a condensing region positioned away from the exhaust system to release thermal energy to the atmosphere. Further, the phase changing materials of the heat pipe may be selected such that thermal energy is absorbed after catalytic converter light-off is achieved. This configuration enables heat transfer without necessarily requiring the use of pumps or other mechanical components. Further, this configuration enables the level of heat transfer to be adjusted without requiring input from a control system, although adjustment via input from a control system may be advantageously used. Further, by taking advantage of the recovered exhaust heat, various other systems may be provided with heat if desired.
Note that one or more heat pipes including phase changing materials may be utilized. Further, the one or more heat pipes may be coupled to and/or integrated with various regions of the exhaust system either directly or indirectly to transfer excessive heat away from the exhaust system. Further still, various different phase changing materials with various different thermal properties may be incorporated, if desired. Therefore, one or more heat pipes may be tailored to recover heat from the exhaust system upstream from the catalytic converter without adversely affecting catalytic converter light-off.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.